Ferroelectric assemblies

ABSTRACT

Some embodiments include ferroelectric assemblies. Some embodiments include a capacitor which has ferroelectric insulative material between a first electrode and a second electrode. The capacitor also has a metal oxide between the second electrode and the ferroelectric insulative material. The metal oxide has a thickness of less than or equal to about 30 Å. Some embodiments include a method of forming an assembly. A first capacitor electrode is formed over a semiconductor-containing base. Ferroelectric insulative material is formed over the first electrode. A metal-containing material is formed over the ferroelectric insulative material. The metal-containing material is oxidized to form a metal oxide from the metal-containing material. A second electrode is formed over the metal oxide.

TECHNICAL FIELD

Ferroelectric assemblies and methods of forming ferroelectricassemblies. In some applications, ferroelectric capacitors and methodsof forming ferroelectric capacitors.

BACKGROUND

Capacitors are electrical components that may be used in integratedcircuitry. A capacitor has two electrical conductors separated byelectrically insulating material. Energy as an electric field may beelectrostatically stored within such material.

A ferroelectric capacitor has ferroelectric material as at least part ofthe insulating material. Ferroelectric materials are characterized byhaving two stable polarized states. The polarization state of theferroelectric material can be changed by application of suitableprogramming voltages, and remains after removal of the programmingvoltage (at least for a time).

In some applications, capacitors may be utilized in memory/storage. Forinstance, ferroelectric capacitors may be incorporated intoferroelectric random access memory (FeRAM).

FeRAM may have many attractive features, including nonvolatility, lowpower consumption, high-speed operation, etc. However, difficulties areencountered in fabricating highly-integrated memory comprising FeRAM. Itis desired to develop new capacitors suitable for utilization in FeRAM,and new methods of fabricating FeRAM.

Ferroelectric materials may be utilized in other assemblies besidescapacitors. For instance, ferroelectric materials may be utilized inferroelectric field effect transistors (FeFETs) and ferroelectric tunneljunction (FTJ) devices. It is desired to develop improvements which maybe utilized across a broad range of ferroelectric assemblies; including,for example, ferroelectric capacitors, FeFETs and FTJ devices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-5 are diagrammatic cross-sectional views of a construction atexample process stages of an example method for fabricating aferroelectric device.

FIG. 6 is a diagrammatic cross-sectional view of a constructioncomprising an example ferroelectric device.

FIG. 7 is a diagrammatic cross-sectional view of a constructioncomprising an example ferroelectric device.

FIG. 8 is a schematic diagram of an example memory array comprisingferroelectric devices.

FIG. 9 is a schematic diagram of an example memory cell comprising aferroelectric capacitor.

FIG. 10 is a diagrammatic cross-sectional view of a constructioncomprising an example ferroelectric device.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Some aspects include recognition that a problem with conventionalferroelectric capacitors is that there may be oxygen vacancies withinthe ferroelectric material, and particularly along an interface betweenthe ferroelectric material and an upper electrode formed across theferroelectric material. The oxygen vacancies may adversely affectperformance of the ferroelectric capacitors, and in some applicationsmay adversely affect performance of memory/storage (for instance, FeRAM)utilizing the ferroelectric capacitors. Some embodiments include methodsof forming ferroelectric capacitors in which reactive metal is providedacross ferroelectric material and subsequently oxidized, with suchoxidation including flow of oxygen into underlying ferroelectricmaterial to decrease the number of oxygen vacancies within theferroelectric material (or at least within an upper region of theferroelectric material). An upper electrode may then be formed acrossthe oxidized reactive metal, and the ferroelectric material may retaindesired operating characteristics associated with ferroelectric materialhaving relatively few oxygen vacancies along an interface adjacent theupper electrode. The oxidized metal remaining in the final capacitorconstruction may distinguish capacitors formed utilizing the methodologydescribed herein from capacitors formed utilizing conventional methods;and some embodiments include ferroelectric capacitors having oxidizedmetal between at least a portion of an upper electrode and aferroelectric material. The problem of oxygen vacancies may occur inother ferroelectric assemblies besides capacitors (for example, inFeFETs and FTJ devices), and embodiments described herein may besuitable for utilization with a broad range of ferroelectric assemblies.

Example methods and structures are described with reference to FIGS.1-10.

FIGS. 1-5 describe an example process for fabricating exampleferroelectric assemblies.

Referring to FIG. 1, a construction 10 comprises an electrode 14supported by a base 12.

The base 12 may comprise semiconductor material; and may, for example,comprise, consist essentially of, or consist of monocrystalline silicon.The base 12 may be referred to as a semiconductor substrate. The term“semiconductor substrate” means any construction comprisingsemiconductive material, including, but not limited to, bulksemiconductive materials such as a semiconductive wafer (either alone orin assemblies comprising other materials), and semiconductive materiallayers (either alone or in assemblies comprising other materials). Theterm “substrate” refers to any supporting structure, including, but notlimited to, the semiconductor substrates described above. In someapplications, the base 12 may correspond to a semiconductor substratecontaining one or more materials associated with integrated circuitfabrication. Such materials may include, for example, one or more ofrefractory metal materials, barrier materials, diffusion materials,insulator materials, etc.

A gap is shown between the base 12 and the electrode 14. Such gap isutilized to diagrammatically indicate that there may be additionalstructures or materials provided between the base 12 and the electrode14. For instance, in some applications the electrode 14 may beincorporated into a ferroelectric capacitor which is one of numeroussubstantial identical ferroelectric capacitors within a memory array(with the term “substantially identical” meaning identical to withinreasonable tolerances of fabrication and measurement). The individualcapacitors may be electrically coupled with transistors, and may beaccessed utilizing digit lines and wordlines. The transistors, digitlines and/or wordlines may be in whole, or at least in part, providedbetween the base 12 and the electrode 14.

The electrode 14 may comprise any suitable composition or combination ofcombinations; such as, for example, one or more of various metals (e.g.,titanium, tungsten, cobalt, nickel, platinum, etc.), metal-containingcompositions (e.g., metal silicide, metal nitride, metal carbide, etc.),and/or conductively-doped semiconductor materials (e.g.,conductively-doped silicon, conductively-doped germanium, etc.). In someembodiments, the electrode 14 may comprise, consist essentially of, orconsist of titanium nitride.

The electrode 14 may have any suitable thickness; and in someembodiments may have a thickness within a range of from about 10angstroms (Å) to about 200 Å.

Referring to FIG. 2, insulative material 16 is formed over the electrode14. The insulative material 16 may be referred to as capacitorinsulative material in some embodiments. At least some of the insulativematerial 16 comprises ferroelectric insulative material, and in someembodiments an entirety of the insulative material 16 is ferroelectricinsulative material.

The ferroelectric insulative material may comprise any suitablecomposition or combination of compositions; and in some exampleembodiments may include one or more of transition metal oxide,zirconium, zirconium oxide, niobium, niobium oxide, hafnium, hafniumoxide, lead zirconium titanate, and barium strontium titanate. Also, insome example embodiments the ferroelectric insulative material may havedopant therein which comprises one or more of silicon, aluminum,lanthanum, yttrium, erbium, calcium, magnesium, strontium, and arare-earth element.

The insulative material 16 may be formed to any suitable thickness; andin some embodiments may have a thickness within a range of from about 30Å to about 250 Å.

Referring to FIG. 3, metal-containing material 18 is formed over theinsulative material 16. In the shown embodiment, oxygen vacancies(represented by the symbol “+”) are within a region of the insulativematerial along an interface with the metal 18. The oxygen vacancies maybe within oxide of the ferroelectric insulative material. Although theoxygen vacancies are shown only along the interface with themetal-containing material 18, it is to be understood that the oxygenvacancies may also extend deeper within the insulative material 16 thanshown in FIG. 3. However, it is generally the oxygen vacancies along theupper interface of the insulative material 16 which are mostproblematic.

The oxygen vacancies may be generated during or after themetal-containing material 18 is formed due to oxygen being pulled frominsulative material 16 to oxidize regions of the metal-containingmaterial 18 adjacent the insulative material 16. Alternatively, theoxygen vacancies may result from other processes. Regardless, the oxygenvacancies may be problematic to the extent that such remain in a finalferroelectric assembly (e.g., capacitor, FeFET, FTJ device, etc.)comprising the insulative material 16.

The metal-containing material 18 may comprise any suitable compositionor combination of compositions; and in some embodiments may comprise,consist essentially of, or consist of one or more of titanium, aluminum,ruthenium, niobium and tantalum. The metal-containing material 18 mayadditionally comprise one or more of nitrogen, carbon, silicon andgermanium.

In some embodiments, it is found that it may be desirable for themetal-containing material 18 to include titanium; and in some exampleembodiments the metal-containing material 18 may comprise, consistessentially of, or consist of titanium.

The metal-containing material 18 may be kept relatively thin; and insome embodiments may have a thickness of less or equal to about 30 Å.For instance, in some embodiments the metal-containing material 18 mayhave a thickness within a range of from about one monolayer to about 20Å. The metal-containing material 18 may be formed to be a continuouslayer (as shown), or may be formed to be a discontinuous film.

Referring to FIG. 4, construction 10 is exposed to oxygen (representedby the symbol “O”), and such oxidizes the metal-containing material 18(FIG. 3) to form a metal oxide 20. The oxygen exposure may compriseexposure of construction 10 to air after forming the metal-containingmaterial 18 (FIG. 3), or may comprise any other suitable exposure (forinstance, exposure to ozone, hydrogen peroxide, etc.). In someembodiments, the metal-containing material 18 is formed within a chamberunder conditions in which oxygen is substantially excluded from beingpresent within an ambient in the chamber; and construction 10 is thenremoved from the chamber and exposed to air to oxidize material 18 andform the oxide 20. Alternatively, or additionally, construction 10 maybe exposed to oxidant in the same chamber utilized to form material 18,with such oxidant being provided after forming material 18; and/or maybe transferred to a second chamber after forming material 18 within afirst chamber, and may then be exposed to oxidant in the second chamber.

Although material 20 is referred to as a metal oxide, in someembodiments the material 20 may be referred to instead as a“metal-containing material which comprises oxygen” to indicate that thematerial 20 may or may not have complete stoichiometric saturation withoxygen. For instance, titanium oxide has the stoichiometric formulaTiO₂; and in some embodiments material 20 may be titanium oxide havingfull stoichiometric saturation with oxygen so that the titanium oxidehas the stoichiometric formula TiO₂, while in other embodiments material20 may be titanium oxide having less than full stoichiometric saturationwith oxygen to that the titanium oxide has the stoichiometric formulaTiO_((2-x)), (where x is a number greater than zero).

Some of the oxygen is transferred to the ferroelectric insulativematerial 16 along an interface adjacent the metal oxide 20, and suchoxygen fills oxygen vacancies within material 16 (represented by areduction of the number of plus symbols (+) in FIG. 4 as compared toFIG. 3); which decreases the amount of oxygen vacancies within theferroelectric insulative material 16.

The metal oxide 20 may, for example, comprise, consist essentially of,or consist of one or more of titanium oxide, aluminum oxide, rutheniumoxide, niobium oxide and tantalum oxide. Additionally, the metal oxide20 may include one or more of nitrogen, carbon, silicon and germanium.In some embodiments, it is found that it can be desirable for the metaloxide 20 to comprise, consist essentially of, or consist of titaniumoxide.

The metal oxide 20 may comprise any suitable thickness; and in someembodiments may have a thickness of less or equal to about 30 Å. Forinstance, the metal oxide 20 may have a thickness within a range of fromabout one monolayer to about 20 Å. The metal oxide 20 may be acontinuous layer in some embodiments, and in other embodiments may be adiscontinuous film.

Referring to FIG. 5, an electrode 22 is formed over the metal oxide 20.In some embodiments, the electrodes 14 and 22 may be referred to asfirst and second electrodes to distinguish the electrodes from oneanother. Either of the electrodes 14 and 22 may be the first electrode,and the other will be the second electrode. Alternatively, theelectrodes 14 and 22 may be referred to as a bottom electrode and a topelectrode, respectively; with the bottom electrode being the electrodewhich is closest to the semiconductor-containing base 12. In someembodiments, the electrodes 14 and 22 may be referred to as capacitorelectrodes. The metal oxide 20 may be between an entirety of theelectrode 22 and the ferroelectric insulative material 16, or may bebetween a portion of the electrode 22 and the ferroelectric insulativematerial 16. Generally, the metal oxide 20 is between at least a portionof the electrode 22 and the ferroelectric insulative material 16.

The electrode 22 may comprise any suitable composition or combination ofcompositions; such as, for example, one or more of various metals (e.g.,titanium, tungsten, cobalt, nickel, platinum, etc.), metal-containingcompositions (e.g., metal silicide, metal nitride, metal carbide, etc.),and/or conductively-doped semiconductor materials (e.g.,conductively-doped silicon, conductively-doped germanium, etc.). In someembodiments, the electrode 22 may comprise, consist essentially of, orconsist of one or more of molybdenum silicide, titanium nitride,titanium silicon nitride, ruthenium silicide, ruthenium, molybdenum,tantalum nitride, tantalum silicon nitride and tungsten.

The electrode 22 may have any suitable thickness, and in someembodiments may have a thickness within a range of from about 10 Å toabout 200 Å.

The electrodes 14 and 22 may comprise a same composition as one anotherin some embodiments, or may comprise different compositions relative toone another. In some embodiments, the electrodes 14 and 22 may bothcomprise, consist essentially of, or consist of titanium nitride.

The electrodes 14 and 22, together with the insulative material 16 andmetal oxide 20 form a ferroelectric assembly 24 (e.g., a ferroelectriccapacitor, an FTJ device, etc.). The ferroelectric assembly 24 may havefew, if any, oxygen vacancies along an interface between theferroelectric insulative material 16 and the metal oxide 20.Accordingly, methodology the type described with reference to FIGS. 1-5may reduce the number of oxygen vacancies within the ferroelectricinsulative material of a ferroelectric assembly as compared toconventional methodologies. The reduced number of oxygen vacancies mayimprove operational aspects of ferroelectric assemblies formed inaccordance with methodologies described herein as compared toferroelectric assemblies formed utilizing conventional methodologies.For instance, it is found that ferroelectric capacitors formed utilizingmethodologies described herein may have improved endurance as comparedto ferroelectric capacitors formed utilizing conventional methodologies;and in some aspects it is found that the ferroelectric capacitors formedutilizing methodologies described herein may have at least about doublethe lifetime relative to analogous ferroelectric capacitors formedutilizing conventional methodologies.

The metal oxide 20 within the ferroelectric assembly 24 of FIG. 5 isshown to be homogeneous. In other embodiments, the metal oxide may beheterogeneous. For instance, an oxygen concentration throughout themetal oxide 20 may be comprised by a gradient. FIG. 6 shows aconstruction 10 a comprising a metal oxide 20 a within a ferroelectricassembly 24 a (e.g., a capacitor, an FTJ device, etc.). The metal oxide20 a is shown having an oxygen gradient extending therethrough, with theoxygen concentration being represented as “[O]”, and with theillustrated gradient (represented by an arrow 21) showing the oxygenconcentration increasing in a direction toward the insulative material16. The oxygen concentration gradient within the metal oxide 20 a mayresult from a reduction of oxygen along an upper surface of the metaloxide 20 a before or during formation of the upper electrode 22, mayresult from increased oxidation of material 20 a along an interface withthe insulative material 16 before or after removal of oxygen vacanciesfrom within the insulative material 16, etc.

The embodiment of FIG. 5 shows the metal oxide 20 as a continuous layer.In other embodiments, the metal oxide may be a discontinuous film. Forinstance, FIG. 7 shows a construction 10 b comprising a metal oxide 20 bwithin a ferroelectric assembly 24 b (e.g., a capacitor, an FTJ device,etc.); and the metal oxide 20 b is configured as a discontinuous film.Openings 23 extend through the discontinuous film of metal oxide 20 b inthe illustrated embodiment. Such openings may be very small; and, forexample, may be pinhole openings in some applications.

In some embodiments, the ferroelectric assemblies described herein(e.g., assembly 24) are capacitors, and such may be incorporated intomemory arrays. An example memory array 50 is described with reference toFIG. 8. The memory array includes a plurality of substantially identicalferroelectric capacitors 24. Wordlines 52 extend along rows of thememory array, and digit lines 54 extend along columns of the memoryarray. Each of the capacitors 24 is within a memory cell 56 which isuniquely addressed utilizing a combination of a wordline and a digitline. The wordlines 52 extend to driver circuitry 58, and the digitlines 54 extend to detecting circuitry 60. In some applications, thememory array 50 may be configured as ferroelectric random access memory(FeRAM).

The memory cells 56 may include transistors in combination with theferroelectric capacitors. For instance, in some applications each of thememory cells 56 may include a transistor 62 in combination with aferroelectric capacitor 24, as shown in FIG. 9. The memory cell 56 isshown coupled with a wordline 52 and a digit line 54. Also, one of theelectrodes of the capacitor 24 is shown coupled with a plate line 64which is utilized in combination with the wordline 52 for controlling anoperational state of the ferroelectric capacitor 24.

The embodiments described above for reducing oxygen vacancies may beutilized relative to ferroelectric capacitors or other assemblies. Forinstance, the assembly 24 of FIG. 5 may correspond to an FTJ device (oranalogously, the assemblies 24 a and 24 b of FIGS. 6 and 7 maycorrespond to FTJ devices). In such embodiments, the material 16 may bea thin layer of ferroelectric material between the electrodes 14 and 22;and the material 20 may be electrically insulative in some applications,or electrically conductive, depending on its desired influence relativeto electrical flow through the assembly. Also, the material 20 may bekept very thin so that it has negligible, or at least nearly negligible)influence on electrical flow through the final structure.

As another example, assemblies analogous to the assemblies 24, 24 a and24 b of FIGS. 5-7 may be utilized as FeFETs, with an example FeFETassembly being shown in FIG. 10 as part of a construction 10 c. Thematerial 16 may be a layer of ferroelectric material between a channelregion 35 and a gate electrode 22. The channel region (which may also bereferred to as a transistor channel region) is between a pair ofsource/drain regions 37 and 39; and all of the regions 35, 37 and 39 arewithin a semiconductor base 33 (with such base 33 comprising anysuitable semiconductor material, such as, for example, silicon,germanium, III/V material, semiconductor oxides, etc.). Persons ofordinary skill in the art will recognize appropriate dopants and/ormaterials for the base 33 and regions 35, 37 and 39. The material 20 ofthe FeFET assembly of construction 10 c may be electrically insulativein some applications, or electrically conductive, depending on itsdesired influence relative to electrical flow through the FeFETassembly. Also, the material 20 may be kept very thin so that it hasnegligible, or at least nearly negligible) influence on electrical flowthrough the final structure.

In some embodiments, the constructions 10-10 b of FIGS. 5-7 show exampleferroelectric capacitors. Although the example capacitors are planarcapacitors (i.e., have planar bottom electrodes), it is to be understoodthat the capacitors may have any suitable configurations; including, forexample, container-type configurations (i.e., may have container-shapedbottom electrodes), pillar-type configurations (i.e., may havepillar-shaped bottom electrodes), etc.

The structures discussed above may be incorporated into electronicsystems. The electronic systems may be any of a broad range of systems,such as, for example, cameras, wireless devices, displays, chip sets,set top boxes, games, lighting, vehicles, clocks, televisions, cellphones, personal computers, automobiles, industrial control systems,aircraft, etc.

Unless specified otherwise, the various materials, substances,compositions, etc. described herein may be formed with any suitablemethodologies, either now known or yet to be developed, including, forexample, atomic layer deposition (ALD), chemical vapor deposition (CVD),physical vapor deposition (PVD), etc.

The terms “dielectric” and “insulative” may be utilized to describematerials having insulative electrical properties. The terms areconsidered synonymous in this disclosure. The utilization of the term“dielectric” in some instances, and the term “insulative” (or“electrically insulative”) in other instances, may be to providelanguage variation within this disclosure to simplify antecedent basiswithin the claims that follow, and is not utilized to indicate anysignificant chemical or electrical differences.

The particular orientation of the various embodiments in the drawings isfor illustrative purposes only, and the embodiments may be rotatedrelative to the shown orientations in some applications. Thedescriptions provided herein, and the claims that follow, pertain to anystructures that have the described relationships between variousfeatures, regardless of whether the structures are in the particularorientation of the drawings, or are rotated relative to suchorientation.

The cross-sectional views of the accompanying illustrations only showfeatures within the planes of the cross-sections, and do not showmaterials behind the planes of the cross-sections, unless indicatedotherwise, in order to simplify the drawings.

When a structure is referred to above as being “on” or “against” anotherstructure, it can be directly on the other structure or interveningstructures may also be present. In contrast, when a structure isreferred to as being “directly on” or “directly against” anotherstructure, there are no intervening structures present.

Some embodiments include a ferroelectric assembly which has a metaloxide over a ferroelectric insulative material. The metal oxide has athickness of less than or equal to about 30 Å. A metal-containingelectrode is over the metal oxide.

Some embodiments include a capacitor which has ferroelectric insulativematerial between a first electrode and a second electrode. The capacitoralso has a metal oxide between at least a portion of the secondelectrode and the ferroelectric insulative material. The metal oxide hasa thickness of less than or equal to about 30 Å.

Some embodiments include a capacitor which includes ferroelectricinsulative material between a first electrode and a second electrode.The capacitor also includes a metal-containing material between at leasta portion of the second electrode and the ferroelectric insulativematerial. The metal-containing material has a thickness of less than orequal to about 30 Å. The metal-containing material includes oxygen andone or more of titanium, aluminum, ruthenium, niobium and tantalum.

Some embodiments include a method of forming an assembly. Ferroelectricinsulative material is formed over a semiconductor-containing base. Ametal-containing material is formed over the ferroelectric insulativematerial. The metal-containing material is oxidized to form a metaloxide from the metal-containing material. An electrode is formed overthe metal oxide.

In compliance with the statute, the subject matter disclosed herein hasbeen described in language more or less specific as to structural andmethodical features. It is to be understood, however, that the claimsare not limited to the specific features shown and described, since themeans herein disclosed comprise example embodiments. The claims are thusto be afforded full scope as literally worded, and to be appropriatelyinterpreted in accordance with the doctrine of equivalents.

We claim:
 1. A capacitor, comprising: ferroelectric insulative material between a first electrode and a second electrode, the ferroelectric insulative material being directly against the first electrode, the ferroelectric insulative material comprising one or more members of the group consisting of zirconium, zirconium oxide, niobium, niobium oxide, hafnium, hafnium oxide, and doped transition metal oxide; and a metal-containing material between at least a portion of the second electrode and the ferroelectric insulative material, the metal-containing material being in direct contact with the second electrode and being in direct contact with the ferroelectric insulative material along an interface, the metal-containing material having an overall thickness of less than or equal to about 30 Å; the metal-containing material including oxygen and at least one metal, the at least one metal consisting of one or more of titanium, aluminum, ruthenium, niobium and tantalum; the oxygen being present at differing concentrations through a thickness of the metal-containing material, with an concentration increasing toward the interface with the ferroelectric insulative material.
 2. The capacitor of claim 1 wherein the capacitor is supported by a semiconductor-containing base; and wherein the first electrode is a bottom electrode and the second electrode is a top electrode, with the bottom electrode being closer to the semiconductor-containing base than the top electrode.
 3. The capacitor of claim 2 wherein the metal-containing material includes one or more nitrogen, carbon, silicon and germanium.
 4. The capacitor of claim 2 wherein the metal-containing material includes titanium and oxygen.
 5. The capacitor of claim 4 wherein the first and second electrodes comprise titanium nitride.
 6. The capacitor of claim 1 being one of a plurality of substantially identical capacitors within a memory array.
 7. The capacitor of claim 1 wherein the metal-containing material is a discontinuous film having openings extending therethrough.
 8. The capacitor of claim 7 wherein the second electrode comprises an electrode material that extends within the openings and contacts the ferroelectric insulative material along a base of the openings. 